The invention relates to the process for the continuous manufacture of electrodes which are used in electric arc furnaces.
Elemental silicon is obtained in a submerged electric arc furnace by reducing quartz with several classes of coals, according to the simplified reaction SiO.sub.2 +2C.fwdarw.Si+2CO. An arc jumps between the electrode and the furnace sole, which generates the necessary energy to carry out this solid-solid reaction process.
When the electric arc jumps between the electrode and the sole, a gradual and continuous consumption of the electrode is produced, which forms a part of the reaction of the metal production. The electrode gradually moves downward within the furnace, and must be replaced from above by a continuous process in which a SODERBERG paste is introduced into a metal casing to produce a self-baking electrode. In this process, the paste melts, solidifies, slips and burns out.
As the electrode is consumed, the metal casing melts and introduces impurities, particularly iron, into the furnace, making it impossible to manufacture high purity elemental silicon.
An attempt to avoid this problem is disclosed in U.S. Pat. No. 4,575,856, corresponding to Spanish Patent 543259, in which a central core or nucleus made of graphite is used, and replacement of the consumed electrode is made by extrusion through the metal casing so that the casing does not burn out and contaminate. The electrode body is formed from several cylindrical sections which are united at the ends, and the metal casing has flat and uniform sides in its cross-section.